1. Filed of the Invention
The present invention relates to a PTO control system to be provided in a work vehicle such as a tractor for transmitting engine power to an external work implement through a PTO (power take-off) transmission system.
2. Description of the Related Art
The above-noted work vehicle is provided with a propelling transmission system for transmitting engine power to drive wheels through a transmission, and the above-noted PTO transmission system. An independent PTO mode and an interlock PTO mode are known as a PTO drive control mode. In the independent PTO mode, a PTO clutch is independently engageable or disengageable regardless of the state of engine power transmission in the propelling transmission system, that is, regardless of whether power transmission is established or broken, which allows power transmission to the work implement to be controlled whether the vehicle is stopped or not. In the interlock PTO mode, control is performed such that the power transmission state of the PTO transmission system is interlocked with the engine power transmission state of the propelling transmission system. Thus, when power transmission in the propelling transmission system is broken, power transmission in the PTO transmission system is also broken, and when power transmission in the propelling transmission system is established, power transmission in the PTO transmission system is also established.
In using the external work implement, some operations are performed preferably in the independent PTO mode and other operations are performed preferably in the interlock PTO mode. Thus, a PTO clutch control device selectable between those modes is known from Japanese Unexamined Utility Model Application Publication No. 63-165241. The PTO clutch control device is provided with a PTO input switch and a mode selection switch. The mode is switchable by the mode selection switch between the interlock PTO mode for disengaging or engaging the PTO clutch in response to a depressing operation or a depression releasing operation of a clutch pedal, and the independent PTO mode for engaging the PTO clutch regardless of the depressing operation of the clutch pedal. This PTO clutch control device allows a PTO clutch solenoid to be driven to engage the PTO clutch when the mode selection switch is moved from the interlock PTO mode to the independent PTO mode with the PTO input switch being turned on. When the mode selection switch is moved to the interlock PTO mode, the PTO clutch is disengaged or engaged in response to the depressing operation or the depression releasing operation of the clutch pedal.
The conventional art disclosed in Japanese Unexamined Utility Model Application Publication No. 63-165241 is disadvantageous in that the PTO clutch in the disengaged state is inadvertently engaged in response to the depressing operation of the clutch pedal to rotate a PTO transmission shaft when the mode selection switch is moved from the interlock PTO mode to the independent PTO mode with the PTO input switch being turned on. In order to avoid such a disadvantage, another PTO clutch control device has been proposed in Japanese Unexamined Patent Application Publication No. 2007-161025 (paragraphs 0002-0007; FIG. 1) which is provided with the PTO input switch and the mode selection switch and switchable by the mode selection switch between the interlock PTO mode for disengaging or engaging the PTO clutch in response to the depressing operation or the depression releasing operation of the clutch pedal, and the independent PTO mode for engaging the PTO clutch regardless of the depressing operation of the clutch pedal. This PTO clutch control device includes disengaged state-maintaining means. When the mode selection switch is moved from the interlock PTO mode to the independent PTO mode with the PTO input switch being turned on, the disengaged state-maintaining means is adapted to maintain the PTO clutch in the disengaged state until the PTO input switch is turned off and then turned on. This arrangement in which the disengaged state-maintaining means is adapted to maintain the PTO clutch in the disengaged state until the PTO input switch is turned off and then turned on eliminates the disadvantage that the PTO clutch is inadvertently engaged to rotate the PTO transmission shaft. However, such a device only having the function of maintaining the PTO clutch in the disengaged state until the PTO input switch is turned off and then turned on after the mode selection switch is moved from the interlock PTO mode to the independent PTO mode cannot necessarily serve the purpose of the operation having a variety of use of the versatile external work implement.